Hydraulic power translating device

ABSTRACT

A hydraulic power translating device of the gerotor type having inner and outer rotatable partially meshing gear elements with a pressure fluid passage surrounding a major part of the exterior periphery of the outer gear element to obtain radial balance of the outer gear element upon start up in motor operation and with a plurality of recesses formed in the case of the device and at the cross-over areas which operate as fluid accumulators of limited capacity to reduce the noise of operation of the device as well as torque variations and to compensate for tolerance and natural frequency variations in the mechanical structure and to also axially balance the gear elements.

O United States Patent 11 1 1111 3,834,842 Dorfl et a1. Sept. 10, 1974[54] HYDRAULIC POWER TRANSLATING 3,427,983 2/1969 Brundage 418/171DEVICE 3,680,989 8/1972 Brundage 418/171 X [75] Inventors: Donald R.Dorff, Union Grove; iprima ry Exammer-W1ll1am L. Freeh 3. Sana Racmeboth of Assistant Examiner-Michael Koczo, Jr.

Attorney, Agent, or FirmWegner, Stellman, McCord, [73] Assignee:Hydraulic Products Incorporated, Wiles & Wood Sturtevant, Wis.

22] Filed: Dec. 6, 1971 ABSTRACT [21] AppL NOJ 205,164 A hydraulic powertranslating device of the gerotor type havmg mner and outer rotatablepartially meshing gear elements with a pressure fluidv passage sur- U.S-

rounding a major part of the exterior periphery of the 418/189 outergear element to obtain radial balance of the uter gear element upon tartup in motor operation 1 Field Of Search 413/166, 171, and with aplurality of recesses formed in the case of 413/79 the device and at thecross-over areas which operate as fluid accumulators of limited capacityto reduce the References C'ted noise of operation of the device as wellas torque vari- UNITED STATES PATENTS ations and to compensate fortolerance and natural 1,793,577 2/1931 Wilsey 418/75 frequenc!variations in the mechanical Structure and 3,007,418 11/1961Brundage..... 418/ 189 X to also axially balance the gear elements.3,034,448 5/1962 Brundage..... 418/189 X 3,303,792 2/1967 Littlewood418/189 10 3 Drawmg Flgures PATENIEDSEPWIBM Sama -a2 SHEEY a {I}? 2HYDRAULIC POWER TRANSLATING DEVICE BACKGROUND OF THE INVENTION Thisinvention pertains to hydraulic power translating devices and, moreparticularly, to a hydraulic pump or motor of the gear type andparticularly the gerotor type with partially meshing inner and outergear elements rotatable within a case and with the outer gear elementbeing eccentric of the inner gear element and to improvements thereinproviding for smoother, quieter operation with reduction .in torquevariations and with provision for improvement in starting torque whenthe device is used as a motor.

A gerotor type of pump or motor is well-known. Existing units have had aresistance to starting when used as a motor. This has resulted from aradial imbalance of forces on the outer gear element when fluid pressureis applied to the motor with the result that the outer gear elementtends to bind against the adjacent wall of the case. Additionally, suchdevices when used as a pump have been noisy in operation and have hadtorque variations with these conditions resulting from the trappedcondition of fluid in the cross-over areas of the device. The foregoingshortcomings of the prior art devices are overcome by the inventiondisclosed herein.

SUMMARY An object of this invention is to provide a new and improvedhydraulic power translating device which overcomes the shortcomings ofthe prior art in providing for a smoother, quieter operating device andwhich when used as a motor has improved starting torque characteristics.

Another object of the invention is to provide a hydraulic powertranslating device wherein the improvements in the starting torquecharacteristics of the device when used as a motor are provided by meanssubjecting the peripheral exterior of the outer gear element to fluidpressure by means of a limited fluid flow giving a controlled pressuredrop to obtain radial balance thereof upon initial start-up of themotor.

Another object of the invention is to provide a hydraulic powertranslating device as defined in the preceding paragraphs wherein theimproved sound and operating characteristics are provided by accumulatormeans of limited capacity positioned at the cross-over areas whichcommunicate with opposite sides of both the inner and outer gearelements of the device as well as any space existing therebetweenwhereby fluid pressure is applied to the opposite sides of said gearelements for axial balance thereof and the accumulator means provide forutilization of the bulk modulus of the fluid to effectively providevariation in the total space confining the fluid in the cross-overareas.

A further object of the invention is to provide a hydraulic translatingdevice as defined in the preceding paragraph of the gerotor type whereinthe radial balancing of the outer gear element and the provision ofaccumulator means are provided by simple machining operations on thecase of the device to provide flow passages from the inlet and outletports of the device to the space exteriorly of the outer gear elementand to provide relatively small cavities formed in the walls of the caseat opposite sides of the inner and outer gear elements for theaccumulator means.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an elevational view of thehydraulic power translating device with a part thereof being shown as asection taken generally along the: line ll in FIG. 2;

FIG. 2 is a vertical section, taken generally along the line 2-2 in FIG.1; and

FIG. 3 is a section, taken generally along the line 3-3 in FIG. 2.

DESCRIPTION OF THE PREFERRED EMBODIMENT The hydraulic power translatingdevice is shown in particular in FIGS. 1 and 2 wherein a multi-part casehas outer parts and .11 mounting a case ring 12 therebetween with afluid seal between the parts being provided by O-rings l4 and 15. Thecase ring 12 of the case is aligned with outer case part 1 0 by a seriesof aligning pins and with there being a series of bolts 21 extendingbetween the outer case parts l0, l1 and through the case ring 12 to holdthe case in fluid-tight assembled relation. The outer case parts 10 and11 each have a bearing 25 and 26, respectively, rotatably mounting ashaft which is a drive shaft when the device is operating as a pump andwhich is an output shaft when the device is operating as a motor.

Disposed between the outer case parts 10 and 11 and surrounded by thecase ring 12 are a pair ofgear elements of the gerotor type. Theseelements include an inner gear element which is keyed to the shaft30 andis concentric with the axis of rotation of the shaft. The second elementis an outer gear element 36 which is rotatably mounted within a chamberdefined by opposed faces of the outer case parts 10 and 11 and by aninternal wall 37 of the case ring 12. This internal wall is cylindrical,but has its center offset eccentrically from the axis of rotation of theshaft 30 and the inner gear element 35. This is conventional in agerotor-type hydraulic power translating device. With the six teeth 40on the inner gear element 35 and the seven internal teeth 41 on theouter gear element 36 there is thus established a plurality of fluidchambers in spaces between the gear elements.

The outer case part 11 has a pair of fluid passages having threadedopenings 45 and 46 at the outer ends thereof for pipe connections and attheir internal ends are shaped to define a pair of kidney-shaped fluidports in the face of the outer case part 11 adjacent to one side of thegear elements 35 and 36. One of these fluid ports 50 is shown in FIG. Iand in broken'line in FIG. 2. With rotation of the gear elements in aclockwise direction as viewed in FIG. 2, the leading end of the fluidport 50 is at 51, while the terminus thereof is at 52. When the deviceis operating as a pump, this is a suction port connected to a source offluid. The second fluid port is shown in broken line in FIG. 2 and, withthe direction of rotation of the gear elements as set forth above, has aleading end 56 and a terminus 57. In the pump application, this is the[pressure port. The relation of the gear elements provides for twocross-over areas wherein fluid communication between the fluid ports 50and 55 is blocked as well as communication between fluid chambers whichare then in fluid communication with the respective fluid ports.

In FIG. 2, a tooth 41a of the outer gear element 36 is shown in closerelation with the mating tooth space of the inner gear element at onecross-over area. The other cross-over area is defined by engagement of apair of teeth a and 40b of the inner gear element 35 with teeth 41b and410 of the outer gear element 36. Again with the rotation of the gearelements in a clockwise direction, there is a gradually increasing spacebetween the gear elements in moving from the cross-over area defined bytooth 41a of the outer gear element to the other cross-over area to drawfluid into the pump and with the fluid chambers beyond the lattercrossover area gradually decreasing in size to pump fluid from thedevice until they reach the cross-over area having tooth 41a.

As is well known, the fluid connections to the device can be reversed tohave the fluid port 50 connected to a source of fluid under pressurewhereby the device will function as a motor to drive the output shaft30.

The face of the outer case part 10 is provided with kidney-shapedrecesses 60 and 61 shaped similarly to the fluid ports 50 and 55 tobalance forces acting on the gear elements because of the fluid ports 50and 55.

When the hydraulic power translating device is operated as a motor withpressure fluid supplied to port 50, there is a hydrostatic conditionexisting on start-up wherein the forces applied hydraulically to thegear elements resultingly force the outer gear element 36 generally inthe direction of the arrow A, shown in FIG. 2. This tends to bind theouter gear element 36 on startup. Improvements in starting torque areobtained by exerting fluid pressure on the exterior periphery of thegear element 36. The pressure is applied on the exterior of the outergear element by a restricted fluid flow through a conducting passagesurrounding the outer gear element and defined therewith by the adjacentfaces of the outer case parts 10, 11 and the wall 37 of the case ring12. The restricted flow provides a controlled pressure drop to obtainradial balance of the outer gear element 36 by the particular locationof the entry and exit points of the fluid flow into the path partiallysurrounding the outer gear element 36. As shown particularly in FIGS. 1and 2, the fluid port 50 is the pressure port when the device isoperating as a motor and a passage 70 connects the inlet opening with arecess 71 formed in the internal wall 37 of the case ring 12. Controlledlimited flow then passes about the exterior of the outer gear element 36until the flow reaches a recess 72 formed on the internal wall 37 of thecase ring 12. The recess 72 communicates with the fluid outlet 46through a passage 73 in the outer case part 11.

The film of fluid rolls with the outer gear element 36 and moves thelatter element away from the case ring 12.

The location of recesses 71 and 72 is approximately coincident with thebeginning 51 of fluid port and the terminus 57 of fluid port 55. Withthe entry of pressure at location 71 there is a force acting inopposition to the lockup force represented by arrow A.

The hydraulic power translating device also has improved structureproviding for reduced torque variations or torque ripple with quieter,smoother operation. This structure is in the form of accumulator meansof limited capacity defined by a series of recesses formed in the facesof outer case parts 10 and 11. These are arranged to axially balance theinner-and outer gear elements. The accumulator means is in the form ofthree pairs of recesses with one recess of each pair being formed in theouter case part 10 and the other recess of each pair being formed in theouter case part 11. These pairs of recesses are shown in FIG. 3 with afirst pair of recesses being identified at and 81, the second pair at 82and 83, and the third pair at 84 and 85. with the recesses 80, 82 and 84being in outer case part 10 and recesses 81, 83, and being in outer casepart 1 l.

The pair of recesses 80 and 81 are located in the cross-over area havingthe tooth 41a of the outer gear element 36 and with the center of thecircularlydimensioned recess being centered on the root diameter of theinner gear element 35 whereby fluid within the recesses 80 and 81 actequally upon generally equal areas of the sides of both the inner andouter gear elements.

The second and third pair of recesses are at the other cross-over area.The pair of recesses 82 and 83 are centered on the root diameter of theinner gear element 35, while the third pair of recesses 84 and 85 arecentered at the root diameter of the outer gear element 36. The pairs ofrecesses communicate with the fluid chambers at the cross-over areaswherein trapped fluid is subjected to compression as well as cavitation.The pairs of recesses provide additional fluid-holding areas wherein thebulk modulus of fluid held therein can function to provide anaccumulator action to compensate for compression, cavitation, andtolerance and natural frequency variations in the mechanical structure.Additionally, the recesses function as balancing ports to provide axialbalance for the inner and outer gear elements 35 and 36.

The capacity of the recess pairs 82-85 must be limited to afluid-holding capacity since, if too large, the action provided therebywould be too slow (in trying to control the rate of compression) andresult in a sloppy system.

The recesses must be of sufficient capacity whereby the total effect ofthe bulk modulus of the fluid will provide the desired results. By testit has been found that satisfactory operation will occur if recesses82-85 have a total fluid volume in a range generally 3-20 percent of thevolume of a fluid chamber of maximum size, with optimum capacity beingpreferably in the range of 5-l0 percent.

The pairs of recesses 80-85 are out of communication with the fluidports 50 and 55 at all times. The series of recesses formed in each ofthe case parts lie along a line which is radial of the shaft 30 andinner gear element 35 and which is also the line along which the gearelements are eccentrically offset.

We claim:

1. A hydraulic power translating device comprising, a case, partiallymeshing inner and outer gear elements rotatably mounted in said casewith said outer gear element being internally toothed and eccentricallymounted relative to the inner gear element whereby a series of fluidchambers are defined between said gears and with said gears having theirteeth interrelated at two cross-over areas wherein fluid communicationis blocked between said fluid chambers at either side of said cross-overareas, a pair of kidney-shaped fluid ports in said case intermediatesaid cross-over areas, means subjecting the circumferential exterior ofsaid outer gear to fluid pressure to obtain radial balance thereof, andaccumulator means positioned at said cross-over areas communicating withopposite sides of both the inner and outer gear elements and with thespace defined therebetween whereby said elements are axially balancedand noise of operation is reduced as well as torque variations.

2. A hydraulic power translating device as defined in claim 1 whereinsaid device is a motor and said means for obtaining radial balance ofthe outer gear element includes means defining a restricted fluid flowpath from the fluid port receiving pressure fluid to the outlet fluidport with said path extending around the exterior of the outer gearelement from a location near the leading end of the pressure fluid portto a location near the terminus of the outlet fluid port.

3. A hydraulic power translating device as defined in claim 2 whereinsaid restricted fluid flow path includes a pair of passages in said caseextending one from each of said fluid ports and each communicating withone of a pair of recesses formed one at each of said locations in a partof the case surrounding said outer gear.

4. A hydraulic power translating device as defined in claim 1 whereinsaid accumulator means comprises recesses formed in said case.

5. A hydraulic power translating device as defined in claim 1 whereinsaid accumulator means comprises three pairs of recesses with therecesses of a pair being formed in said case at opposite sides of saidgear elements, all three pairs of recesses being in the cross-over areaswith one pair of recesses being centered on the root diameter of theinner gear element at the cross over area where the tip of an outer gearelement tooth and the adjacent root of the mating tooth space of theinner gear element are closely adjacent, the second and third pair ofrecesses being at the other cross-over area, the second pair of recessesbeing centered on the root diameter of the inner gear element and thethird pair of recesses being centered on the root diameter of the outergear element, and all of said recesses at one side of the gear elementslying along a line which is radial of said inner gear element.

6. A hydraulic pump of the gerotor type comprising, a case, an innergear element and an outer gear element rotatably mounted in said casewith said outer gear element eccentrically mounted relative to the innergear element whereby a series of fluid chambers are defined between saidgears and with said gears having their teeth interrelated at twocross-over areas wherein fluid communication is blocked between saidfluid chambers at either side of said cross-over areas, a pair ofkidneyshaped fluid ports intermediate said cross-over areas forcompleting a flow path through the device, and recesses in said case forfluid positioned at said cross-over areas communicating with oppositesides of both the inner and outer gear elements and with the spacedefined therebetween whereby said elements are axially balanced andnoise of operation is reduced as well as torque ripple.

7. A hydraulic power pump as defined in claim 6 wherein there are threepairs of said recesses with a recess of each pair being formed in saidcase at a side of said gear elements, a pair of recesses being atopposite sides of said gear elements, all three pairs of recesses beingin the cross-over areas with one pair of recesses being centered on theclosely adjacent tip of an outer gear element tooth and the adjacentroot of the mating tooth space of the inner gear element at onecross-over area, a second pair of recesses being bisected by a matingtooth space on the inner gear element, the third pair of recesses beingbisected by a mating tooth space of the outer gear element, and the lasttwo pairs of recesses being at the other cross-over area.

8. A hydraulic power pump as defined in claim 7 wherein the last twopairs of recesses are generally circular limited depth recesses to holda limited amount of fluid in the range of generally 3-20 percent of thevolume of a maximum fluid chamber size and preferably in the range of5-10 percent.

9. A hydraulic pump of the gerotor type as defined in claim 6 whereinthere are three pairs of said recesses of limited size with the recessesof a pair being formed in said case at opposite sides of said gearelements, all three pairs of recesses being in the cross-over areas withone pair of recesses being centered on the root diameter of the innergear element at the cross-over area where the tip of an outer gearelement tooth and the adjacent root of the mating tooth space of theinner gear element are closely adjacent, the second and third pair ofrecesses being at the other cross-over area the second pair of recessesbeing centered on the root diameter of the inner gear element and thethird pair of recesses being centered on the root diameter of the outergear element, the second and third pair of recesses having a totalvolume of approximately 10 percent of the volume of a fluid chamber ofmaximum size, and all of said recesses at one side of the gear elementslying along a line which is radial of said inner gear element.

10. A hydraulic pump of the gerotor type comprising, a case, an innergear element and an outer gear element rotatably mounted in said casewith said outer gear element eccentrically mounted relative to the innergear element whereby a series of fluid chambers are defined between saidgears and with said gears having their teeth interrelated at twocross-over areas wherein fluid communication is blocked between saidfluid chambers at either side of said cross-over areas, a pair ofkidneyshaped fluid ports intermediate said cross-over areas, a pair ofrecesses formed in said case at one of said crossover'areas, twoadditional pairs of recesses in said case at the other of saidcross-over areas where there is a maximum size fluid chamber, all ofsaid recesses communicating with opposite sides of both the inner andouter gear elements and with the space defined therebetween whereby saidelements are axially balanced and said recesses provide small fluidaccumulators to reduce the noise of operation as well as torquevariations.

1. A hydraulic power translating device comprising, a case, partiallymeshing inner and outer gear elements rotatably mounted in said casewith said outer gear element being internally toothed and eccentricallymounted relative to the inner gear element whereby a series of fluidchambers are defined between said gears and with said gears having theirteeth interrelated at two cross-over areas wherein fluid communicationis blocked between said fluid chambers at either side of said cross-overareas, a pair of kidney-shaped fluid ports in said case intermediatesaid cross-over areas, means subjecting the circumferential exterior ofsaid outer gear to fluid pressure to obtain radial balance thereof, andaccumulator means positioned at said cross-over areas communicating withopposite sides of both the inner and outer gear elements and with thespace defined therebetween whereby said elements are axially balancedand noise of operation is reduced as well as torque variations.
 2. Ahydraulic power translating device as defined in claim 1 wherein saiddevice is a motor and said means for obtaining radial balance of theouter gear element includes means defining a restricted fluid flow pathfrom the fluid port receiving pressure fluid to the outlet fluid portwith said path extending around the exterior of the outer gear elementfrom a location near the leading end of the pressure fluid port to alocation near the terminus of the outlet fluid port.
 3. A hydraulicpower translating device as defined in claim 2 wherein said restrictedfluid flow path includes a pair of passages in said case extending onefrom each of said fluid ports and each communicating with one of a pairof recesses formed one at each of said locations in a part of the casesurrounding said outer gear.
 4. A hydraulic power translating device asdefined in claim 1 wherein said accumulator means comprises recessesformed in said case.
 5. A hydraulic power translating device as definedin claim 1 wherEin said accumulator means comprises three pairs ofrecesses with the recesses of a pair being formed in said case atopposite sides of said gear elements, all three pairs of recesses beingin the cross-over areas with one pair of recesses being centered on theroot diameter of the inner gear element at the cross-over area where thetip of an outer gear element tooth and the adjacent root of the matingtooth space of the inner gear element are closely adjacent, the secondand third pair of recesses being at the other cross-over area, thesecond pair of recesses being centered on the root diameter of the innergear element and the third pair of recesses being centered on the rootdiameter of the outer gear element, and all of said recesses at one sideof the gear elements lying along a line which is radial of said innergear element.
 6. A hydraulic pump of the gerotor type comprising, acase, an inner gear element and an outer gear element rotatably mountedin said case with said outer gear element eccentrically mounted relativeto the inner gear element whereby a series of fluid chambers are definedbetween said gears and with said gears having their teeth interrelatedat two cross-over areas wherein fluid communication is blocked betweensaid fluid chambers at either side of said cross-over areas, a pair ofkidney-shaped fluid ports intermediate said cross-over areas forcompleting a flow path through the device, and recesses in said case forfluid positioned at said cross-over areas communicating with oppositesides of both the inner and outer gear elements and with the spacedefined therebetween whereby said elements are axially balanced andnoise of operation is reduced as well as torque ripple.
 7. A hydraulicpower pump as defined in claim 6 wherein there are three pairs of saidrecesses with a recess of each pair being formed in said case at a sideof said gear elements, a pair of recesses being at opposite sides ofsaid gear elements, all three pairs of recesses being in the cross-overareas with one pair of recesses being centered on the closely adjacenttip of an outer gear element tooth and the adjacent root of the matingtooth space of the inner gear element at one cross-over area, a secondpair of recesses being bisected by a mating tooth space on the innergear element, the third pair of recesses being bisected by a matingtooth space of the outer gear element, and the last two pairs ofrecesses being at the other cross-over area.
 8. A hydraulic power pumpas defined in claim 7 wherein the last two pairs of recesses aregenerally circular limited depth recesses to hold a limited amount offluid in the range of generally 3-20 percent of the volume of a maximumfluid chamber size and preferably in the range of 5-10 percent.
 9. Ahydraulic pump of the gerotor type as defined in claim 6 wherein thereare three pairs of said recesses of limited size with the recesses of apair being formed in said case at opposite sides of said gear elements,all three pairs of recesses being in the cross-over areas with one pairof recesses being centered on the root diameter of the inner gearelement at the cross-over area where the tip of an outer gear elementtooth and the adjacent root of the mating tooth space of the inner gearelement are closely adjacent, the second and third pair of recessesbeing at the other cross-over area the second pair of recesses beingcentered on the root diameter of the inner gear element and the thirdpair of recesses being centered on the root diameter of the outer gearelement, the second and third pair of recesses having a total volume ofapproximately 10 percent of the volume of a fluid chamber of maximumsize, and all of said recesses at one side of the gear elements lyingalong a line which is radial of said inner gear element.
 10. A hydraulicpump of the gerotor type comprising, a case, an inner gear element andan outer gear element rotatably mounted in said case with said outergear element eccentricaLly mounted relative to the inner gear elementwhereby a series of fluid chambers are defined between said gears andwith said gears having their teeth interrelated at two cross-over areaswherein fluid communication is blocked between said fluid chambers ateither side of said cross-over areas, a pair of kidney-shaped fluidports intermediate said cross-over areas, a pair of recesses formed insaid case at one of said cross-over areas, two additional pairs ofrecesses in said case at the other of said cross-over areas where thereis a maximum size fluid chamber, all of said recesses communicating withopposite sides of both the inner and outer gear elements and with thespace defined therebetween whereby said elements are axially balancedand said recesses provide small fluid accumulators to reduce the noiseof operation as well as torque variations.